EBay is getting into the radio advertising business, becoming a broker of ad spots and on its way to competing with Google, which provides a similar service.The new service will go live today as part of the eBay Media Marketplace.The radio ad brokerage service will be powered by Bid4Spots. Advertisers and ad agencies can register on the eBay Media Marketplace Web site now.The service will make available "prime" inventory from more than 2300 radio stations.Like Google, eBay will use the Internet to attempt to improve the way these radio ads are bought and sold, and the way radio marketing campaigns are tracked and analyzed.